1. Field of the Invention
The present invention relates to methods of consolidating unconsolidated weak zones or formations formed of clays, shales, sand stone and the like and forming a chemical casing in a well bore penetrating the weak zones or formations.
2. Description of the Prior Art
Rotary drilling methods are commonly utilized in the drilling of oil and gas wells. That is, the well bore which extends from the surface into one or more subterranean oil and/or gas producing formations is drilled by a rotary drilling rig on the surface which rotates a drill bit attached to a string of drill pipe. The drill bit includes rotatable cutting surfaces so that when the drill bit is rotated by the drill string against subterranean strata under pressure a bore hole is produced.
A drilling fluid is circulated downwardly through the drill string, through the drill bit and upwardly in the annulus between the walls of the well bore and the drill string. The drilling fluid functions to maintain hydrostatic pressure on formations penetrated by the well bore and to remove cuttings from the well bore. As the drilling fluid is circulated, a filter cake of solids from the drilling fluid forms on the walls of the well bore. The filter cake build-up is a result of initial fluid loss into permeable formations and zones penetrated by the well bore. The presence of the filter cake reduces additional fluid loss as the well is drilled.
In addition to removing cuttings from the well bore and forming filter cake on the well bore, the drilling fluid cools and lubricates the drill bit and exerts a hydrostatic pressure against the well bore walls to prevent blow-outs, i.e., to prevent pressurized formation fluids from flowing into the well bore when formations containing the pressurized fluids"" are penetrated. The hydrostatic pressure created by the drilling fluid in the well bore may fracture low mechanical strength formations penetrated by the well bore which allows drilling fluid to be lost into the formations. When this occurs, the drilling of the well bore must be stopped and remedial steps taken to seal the fractures which are time consuming and expensive.
In order to insure that fracturing of low mechanical strength formations penetrated by the well bore and other similar problems do not occur, it has heretofore been the practice to intermittently seal the well bore by cementing pipe referred to in the art as casing or liners in the well bore. The points in the well bore during its drilling at which the drilling is stopped and casing or liners are installed in the well bore are commonly referred to as xe2x80x9ccasing pointsxe2x80x9d. Casing or a liner is placed in the well bore above each casing point and a sealing composition such as a hydraulic cement composition is pumped into the annular space between the walls of the well bore and the exterior surface of the casing or liner disposed therein. The hydraulic cement composition is permitted to set in the annulus thereby forming an annular sheath of hardened substantially impermeable cement therein. The cement sheath physically supports and positions the pipe in the well bore and bonds the pipe to the walls of the well bore whereby the undesirable migration of fluids between zones or formations penetrated by the well bore is prevented. This technique of cementing pipe in the well bore as the drilling progresses has a number of disadvantages including the time and expense incurred in placing and sealing the pipe as well as the reduction in the well diameter after each casing point. That is, the well diameter must be reduced below each casing point so that a smaller casing can be lowered through the previously placed casing and sealed in the well bore.
Another problem that occurs in the drilling and completion of well bores is that when the well bore is drilled into and through unconsolidated weak zones or formations formed of clays, shales, sand stone and the like, unconsolidated clay, shale and sand slough off the sides of the well bore which enlarges the well bore and often causes the drill bit and drill pipe to become stuck whereby drilling, must be stopped and remedial steps taken.
Thus, there are needs for improved methods of drilling well bores whereby unconsolidated weak zones or formations are consolidated and the mechanical strength of the well bore is increased during drilling without the need to stop drilling for prolonged periods of time.
By the present invention, methods of consolidating unconsolidated weak zones or formations during drilling are provided. Also, methods of forming a hard and tough chemical casing in a well bore during drilling to increase the mechanical strength of the well bore are provided. The chemical casing formed while drilling also prevents undesirable migration of fluid between zones or formations penetrated by the well bore, generally referred to as xe2x80x9czonal isolation.xe2x80x9d The methods of consolidating unconsolidated weak zones or formations during drilling or forming a hard and tough chemical casing during drilling can be carried out separately or simultaneously.
A method of this invention for consolidating unconsolidated weak zones or formations formed of clays, shales, sand stone and the like while drilling a well bore penetrating the zones or formations to prevent sloughing is as follows. A well bore is drilled with a drilling fluid having a pH in the range of from about 6 to about 10 and comprised of water, a polymeric cationic catalyst capable of accepting and donating protons which is adsorbed on the unconsolidated clays, shales, sand stone and the like, a water soluble or dispersible polymer which is cross-linkable by a thermoset resin and causes the resin to be hard and tough when cured and a water soluble or dispersible thermoset resin which cross-links the polymer, is catalyzed and cured by the catalyst and consolidates the weak zones or formations so that sloughing is prevented.
Another method of this invention for consolidating unconsolidated weak zones or formations formed of clays, shales, sand stone and the like while drilling a well bore penetrating the zones or formations to prevent sloughing is comprised of the following steps. A well bore is drilled with a drilling fluid having a pH in the range of from about 6 to about 10 and comprised of water and a polymeric cationic catalyst capable of accepting and donating protons which is adsorbed on the unconsolidated clays, shales, sand stone and the like. Thereafter, the well bore is contacted with a treating fluid having a pH in the range of from about 6 to about 10 and comprised of water, a water soluble or dispersible polymer which is cross-linkable by a thermoset resin and causes the resin to be hard and tough when cured and a water soluble or dispersible thermoset resin which cross-links the polymer, is catalyzed and cured by the catalyst and consolidates the weak zones or formations so that sloughing is prevented.
A method of this invention for forming a chemical casing in a well bore to improve the mechanical strength thereof and/or prevent undesirable migration of fluids between zones or formations while drilling the well bore is as follows. A well bore is drilled with a drilling fluid having a pH in the range of from about 6 to about 10 and comprised of water, a water soluble or water dispersible polymer which is cross-linkable by thermoset resins and causes the resins to be hard and tough when cured, a particulate curable solid thermoset resin, a water soluble thermoset resin, and a delayed dispersible acid catalyst for curing the solid thermoset resin and the water soluble thermoset resin, the drilling fluid forming a filter cake on the walls of the well bore that cures into a hard and tough cross-linked chemical casing thereon.
A method of this invention for consolidating unconsolidated weak zones or formations formed of clays, shales, sand stone and the like to prevent sloughing and forming a chemical casing in a well bore penetrating the weak zones or formations to improve the mechanical strength of the well bore and/or prevent undesirable migration of fluids between zones or formations while drilling the well bore is as follows. A well bore is drilled with a drilling fluid having a pH in the range of from about 6 to about 10 and comprised of water, a polymeric cationic catalyst capable of accepting and donating protons which is adsorbed on the unconsolidated clays, shales, sand stone and the like, a water soluble or dispersible polymer which is cross-linkable by a thermoset resin and causes the resin to be hard and tough when cured, a particulate curable solid thermoset resin, a water soluble thermoset resin and a delayed dispersible acid catalyst for curing the thermoset resins, the drilling fluid forming a filter cake on the walls of the well bore that cures and consolidates the unconsolidated weak zones and formations penetrated by the well bore so that sloughing is prevented and forms a hard and tough cross-linked chemical casing on the walls of the well bore which prevents the undesirable migration of fluids between zones or formations.
Another method of this invention for consolidating unconsolidated weak zones or formations formed of clays, shales, sand stone and the like to prevent sloughing and forming a chemical casing in a well bore penetrating the weak zones or formations to improve the mechanical strength of the well bore while drilling, the well bore is comprised of the following steps. A well bore is drilled with a drilling fluid having a pH in the range of from about 6 to about 10 and comprised of water, a polymeric cationic catalyst capable of accepting and donating protons which is adsorbed on the unconsolidated clays, shales, sand stone and the like, a particulate curable solid thermoset resin and a delayed acid catalyst for curing the solid thermoset resin, the drilling fluid forming a filter cake on the walls of the well bore that cures and consolidates the unconsolidated weak zones and formations penetrated by the well bore so that sloughing is prevented. Thereafter, the well bore is contacted with a treating fluid comprised of water, a water soluble or dispersible polymer which is cross-linkable by a thermoset resin and causes the resin to be hard and tough when cured and a water soluble or dispersible thermoset resin, the treating fluid components depositing on the filter cake formed by the drilling fluid and the thermoset resin curing into a hard and tough cross-linked chemical casing on the walls of the well bore.
The objects, features and advantages of the invention will be readily apparent to those skilled in the art upon a reading of the description of preferred embodiments which follows.